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Atomic-engineering of noble metal into single-atom electrocatalysts with well-defined active sites has been considered as an effective approach to enhance the mass-activity towards hydrogen evolution reaction (HER), crucial for the practical implementation of this sustainable technology. Herein, we devise a metallic-coordination strategy via a facile one-step pyrolysis method, for the atomic isolation of a small amount of platinum (Pt, 0.45 wt%) atoms in the surface of nickel (Ni) nanoparticles (Pt 1 @Ni) encapsulated into nitrogen-doped carbon nanotubes (Pt 1 @Ni/NCNT). Such a Pt 1 @Ni/NCNT single-atom alloy catalyst exhibits a record-high and all-round superior HER performance including mass-activity (up to 350.7 A mg Pt −1@η 150), stability (>50 h at 100 mA cm−2), pH-tolerance by comparison with Pt 1 @NC. Our density functional theory calculations combined with in situ Raman spectroscopic studies reveal a synergistic dual-active-site catalytic mechanism, involving the fast hydrogen spillover effect on coordinated Ni supports and accelerated water dissociation in acidic and alkaline medium, respectively. A strong electronic hybridization of 5d orbital of alloyed Pt and 3d orbital of Ni atoms modulates the d band center of Pt, which not only boosts HER activity but also stabilizes Pt single atoms. Due to the double protecting strategy from strong anchoring effect in Ni support and chemically stable NCNT shell, a robust stability is achieved for Pt 1 @Ni/NCNT hierarchal catalyst. Our findings open up a new avenue to substantially tailor the activity of surface Pt atoms for the design of highly efficient and durable noble metal-based catalysts. [Display omitted] • Pt single atoms are anchored on metallic Ni nanoparticles. • Pt1@Ni/NCNT exhibits a 146-time higher mass activity than Pt/C in acidic media. • 70-time higher mass activity is recorded for Pt1@Ni/NCNT than Pt/C in alkaline electrolyte. [ABSTRACT FROM AUTHOR]

Hydrogenation of biomass-derived aqueous levulinic acid (LA) to produce γ-valerolactone (GVL) is a promising approach from biomass to sustainable platform chemicals. However, the practical application of this method is limited because aqueous LA is highly corrosive to metal-based hydrogenation catalyst in high-temperature hydrothermal environments. Herein, we encapsulated metallic Ni0 particles with a few layers of graphene using a hydrothermal carbon coating method to obtain Ni@FLG-600 catalyst, which exhibited efficient catalytic activity and excellent cycling stability for the hydrogenation of aqueous LA to GVL. The defect-rich graphene shell prevents the Ni0 from acid corrosion meanwhile selectively permits the passage of small H 2 molecules. The resulted active H* on Ni0 spills over to the outer surface of graphene shell and reacts with LA. Remarkably, the amount of H* on graphene shell can be the descriptor of activity. This finding presents a new strategy for the fabrication of acid-resistant catalysts for aqueous biomass hydrogenation. [Display omitted] • Ni@FLG-600 is synthesized for aqueous hydrogenation of LA to GVL. • Ni0 encapsulated in a few layers of graphene is hydrothermally stable. • The Ni@FLG-600 catalyst can be reused twenty times without deactivation. • H 2 passes through the defects in the graphene shell and is activated to H* on Ni0. • H* spills over to the graphene surface to react with LA. [ABSTRACT FROM AUTHOR]

In hydrodeoxygenation (HDO) reactions, the evolution of the chemical states of active species in the catalyst caused by the spillover effects greatly influences their catalyst performance. Herein, the HDO of guaiacol (GUA) over CuCoO x and CuCoCeO x catalysts synthesized by co-precipitation method was systematically investigated. During the HDO reaction of GUA, acid sites (Co(II)) facilitated the C-O bond (demethylation via -OCH 3) cleavage, which was the rate-determining step. A series of characterizations and experimental results revealed that introducing CeO 2 into the CuCoO x catalyst could enable the catalyst to undergo reverse oxygen spillover in the hydrogenation environment, promoting the regeneration of CoO in the catalyst. Therefore, the deactivation of the CuCoO x catalyst due to hydrogen spillover and CoO reduction could be avoided, and the catalyst stability improved. The present study methodically investigated the spillover effects induced by Cu and CeO 2 and provided the theoretical basis for the structural design of heterogeneous catalysts. [Display omitted] • Guaiacol HDO reaction with C-O bond scission as the rate-determining step. • Construction of CuCoO x -based catalysts with acid sites (Co(II)) as active center. • Utilization of reverse oxygen spillover to improve CuCoO x catalyst stability. • Catalyst deactivation and stability mechanisms discussed based on spillover effects. [ABSTRACT FROM AUTHOR]

Photocatalytic ammonia synthesis is heralded as the most promising field that will certainly gain increasing attention as a sustainable strategy for low-carbon NH 3 production and H 2 storage. However, one great challenge is to design ideal catalysts, which can provide the energetic active sites for nitrogen activation and hydrogen dissociation at the same time. In this study, we report that efficient photo-driven ammonia synthesis can be realized by synergetic effect of abundant Mo (V) species and Pt under ambient conditions. More specifically, the optimized Pt-loaded MoO 3-x photocatalyst has attained the superior NH 3 production rates of 3456 μg·g−1·h−1 under visible light irradiation (≥400 nm). As evidenced experimentally and theoretically, the enhanced photocatalytic performance can be ascribed to dual-active sites, where the loaded Pt co-catalyst can boost hydrogen spillover from Pt to MoO 3-x induced by O V due to the low barrier of H* migration between hydrogen activation sites (Pt-O bridge) and nitrogen activation sites (low-valence Mo species), further increasing the number of Mo (V) active sites. And Mo (V) species adjacent oxygen vacancy with outstanding electron-donating capability and strong nitrogen chemisorption played a crucial role in facilitating nitrogen dissociation. Therefore, synergizing abundant Mo (V) species and loaded-Pt can optimize the photo-driven nitrogen reduction and hydrogen oxidation. This work provides a new idea for the rational design of efficient photo-driven ammonia synthesis. [Display omitted] • The efficient photo-driven ammonia synthesis can be realized by synergetic effect of abundant Mo (V) species and Pt under ambient conditions in the gas-solid system. • The low-valence Mo species offer the more energetic photo-electrons transfer for nitrogen molecule and elevate the conduction band position for nitrogen reduction. • Pt nanoparticles boost hydrogen spillover from Pt to MoO 3-x induced by O V , which increases the number of Mo (V) active sites and promotes the hydrogenation of nitrogen. • · The dual active sites can be conducive to circumvent the scaling relations. [ABSTRACT FROM AUTHOR]

Water adsorption/dissociation and hydrogen intermediates (H*) desorption are the two elementary steps for hydrogen evolution reaction (HER) kinetics. This study builds on the promising concept of planning each step simultaneously to optimize in a whole. Theoretical and experimental approaches are combined to design and synthesize nickel oxide with moderate oxygen vacancy (V O) coating copper nanowires, namely m-V O NiO/Cu, for excellent HER in alkali. The construction of V O expedites H 2 O adsorption and dissociation on NiO, thereby significantly increases H* coverage on the surface. Subsequently, the incorporation of Cu creates accessible H* adsorption sites by limited hydrogen spillover from NiO to Cu, thereby facilitates the desorption of the next hydrogen directly on NiO continuously. The sweet marriage of V O NiO and Cu endows the most promising alkaline HER performance of a 20 mV overpotential at 10 mA cm–2 with a Tafel slope of 39.9 mV dec–1. This work presents a fresh perspective on upgrading multi-step reaction kinetics and encourages further research on advanced earth-abundant catalysts. [Display omitted] • High-efficiency HER electrocatalyst was designed through a sweet marriage of O-defected NiO and Cu. • NiO with appropriate V O concentration accelerates water activation and dissociation. • A limited hydrogen spillover takes place from m-V O NiO to Cu. • The H* absorbed on Cu assists the desorption of the next H* directly on NiO continuously. [ABSTRACT FROM AUTHOR]

This investigation focuses on the catalytic demethoxylation of alkylmethoxyphenols derived from lignin depolymerization, aiming to convert them with high selectivity into essential chemical intermediates, namely methoxy-free alkyl phenols. A silver-loaded iron-cobalt oxide (Ag/Fe-CoO x) nanocomposite catalytic system was developed, featuring a dual-active-site catalytic mechanism driven by a hydrogen-spillover effect that involves the activation of hydrogen at the metallic active site, while the support's secondary site serves as the reaction locus for the substrates. It was revealed that by integrating iron into cobalt oxide nanosheet supports, catalyst activity and selectivity were finely tuned, particularly to enhance the production of demethoxylated phenols. With the optimized Ag/Fe-CoO x catalyst, a 99.7 % conversion of 4-propylguaiacol and a 94.1 % selectivity for 4-propylphenol were achieved, indicating effective reductive demethoxylation at 280°C and 0.4 MPa H 2. The fine structure of the support significantly affects demethoxylation selectivity, guiding the development of selective catalyst design in biomass conversion. [Display omitted] • Ag/Fe-CoO x enhances H 2 spillover for efficient demethoxylation of lignin phenols. • Dual-active-site mechanism and Fe doping are critical for selective control. • Achieves 99.7 % 4-propylguaiacol conversion, 94.1 % selectivity at 280°C, 0.4 MPa H 2. • Ag/Fe-CoO x achieves 94.7 % selective demethoxylation of birch lignin oil. [ABSTRACT FROM AUTHOR]

Despite the fruitful achievements in the development of high-performance catalysts, most of materials still suffer limited HER kinetics and poor durability in harsh acidic media, especially at high current densities. In this work, a Pd nanoparticles/Ir metallene heterojunction structure (Pd/Ir hetero-metallene) were successfully prepared by a facile co-reduction method. The hydrogen spillover bridging H+ adsorption/H 2 desorption process occurring at the Pd/Ir interface results in the rate-determining step change to a Tafel step, which accelerates the HER kinetics. The Pd/Ir hetero-metallene has a relatively low Δ G Hads (-0.19 eV), which allows for rapid adsorption of H+ and release of H 2 , thus greatly improving the performance of HER. As a result, the Pd/Ir hetero-metallene exhibits remarkable HER performance with ultra-low overpotentials of only 69 and 133 mV to reach 500 and 1000 mA cm−2, a small Tafel slope of 21 mV dec−1, and superb stability. [Display omitted] • Pd nanoparticles/Ir metallene hybrid structure were successfully prepared were prepared via a co-reduction method. • The hydrogen spillover bridging H+ adsorption/H 2 desorption process occurring at the Pd/Ir interface. • Pd/Ir hybrid-metallene exhibits ultra-low overpotentials of only 69 and 133 mV to reach 500 and 1000 mA cm−2. • The strategy provides a novel strategy for preparing high-performance HER catalysts. [ABSTRACT FROM AUTHOR]

The development of photocatalysts with desirable compositions and structures to improve the selectivity of CO 2 conversion to hydrocarbon remains a challenging goal. In this study, we present a strategy of defected TiO 2 nanobelts with metastable ordered oxygen vacancies by a simple Pd-catalyzed oxygen reduction method under anoxic condition. Ordered oxygen vacancies not only provide the driving force and channel for the directional movement of photoinduced electrons by modulating built-in electric field, but also promote CO 2 adsorption and activation. Pd nanoparticles (Pd NPs) boosted dissociation of H 2 O to increase H* coverage and promoted the protonation of the intermediates via hydrogen spillover. The synergistic effect of ordered oxygen vacancies and hydrogen spillover contributed to the enhanced photocatalytic reduction of CO 2 toward C 2 products. The maximum selectivity of C 2 products can reach 51.45% with an evolution rate of 25.987 μmol·g−1·h−1. This strategy provides a convenient method for designing a selective CO 2 conversion photocatalyst. [Display omitted] TiO 2 nanobelts with metastable ordered oxygen vacancies were successfully synthesized via a simple Pd-catalyzed oxygen reduction method. Single crystal TiO 2 nanobelts with exposed highly active (110) facet and ordered oxygen vacancies provide more active sites for CO 2 adsorption and activation, and provide an excellent architectural arrangement for accelerating charge carrier transfer. Pd NPs sites with strong electrons capture ability boosted the dissociation of H 2 O to increase H* coverage, which then rapidly migrate to the metal-support interface attributed to hydrogen spillover effect, improving the yield and selectivity of C 2 products. • Defected TiO 2 nanobelts with ordered oxygen vacancies was prepared by Pd-catalyzed oxygen reduction method. • Ordered oxygen vacancies provide channel for directional movement of photoinduced electrons. • Pd nanoparticles boost dissociation of H 2 O to increase H* coverage. • Pd nanoparticles promotthe protonation of the intermediates via hydrogen spillover. • The maximum selectivity of C 2 products can reach 51.45% with an evolution rate of 25.987 μmol•g−1•h−1. [ABSTRACT FROM AUTHOR]

The high recombination of photoinduced electron-hole and deep charge trapping in graphitic carbon nitride (g-C 3 N 4)-based photocatalysts have limited the photocatalytic activity in hydrogen evolution reaction (HER). Here, we proposed the synergistic strategies of electron-deficient boron (B) and electron-rich phosphorus (P) doped g-C 3 N 4 (BPCN) through tuning the electron density for enhanced photocatalytic activity in HER under visible light irradiation. The BPCN exhibited highest photocatalytic activity in HER with the apparent quantum efficiency of 17.4% at 400 nm superior to reported g-C 3 N 4 -based photocatalysts. The remarkable activity in HER was attributed to the efficient charge separtion by the shallow charge capture, electron transfer from P to B and the efficient hydrogen spillover pathway occurred by the strong absorption H 2 O at P sites and then H transferring to B sites. This work paves a new route to changing the electronic density with the tunable band structures through the doping engineering for enhanced photocatalytic activity. [Display omitted] ● Ultrathin two-dimensional B, P codoped g-C 3 N 4 were successfully constructed by the in-situ doping method. ● Electron deficient B and electron rich P regulate the electronic density of ultrathin g-C 3 N 4 for the enhanced photocatalytic HER. ● A new charge transfer channel (P→N→C→B) affects the electron density distribution in the π separation domain of g-C 3 N 4. ● Femtosecond TA measurements demonstrate the long-lived shallow trap state capture of photogenerated electrons. ● An efficient hydrogen spillover pathway indicated the strong absorption of H 2 O at P site and then H* transfer to B site. [ABSTRACT FROM AUTHOR]

The low intrinsic catalytic performance and stability are the two dominant obstacles for alkaline hydrogen evolution reaction (HER) electrocatalyst. Herein, amorphous molybdenum oxide (MoO x) has been introduced to rhodium hierarchical nanosheets (MoO x Rh-HNS) at atomic level efficiently reducing the barrier for hydrogen spillover from Rh to MoO x ; thereby, MoO x Rh-HNS exhibit superior HER activity with mass activity of 23.9 A mg noble metal −1 at overpotential of 200 mV, which is boosted by 10.8- and 14.9-fold with relative to Rh-HNS and Pt/C in alkaline media, respectively. Meanwhile, Tafel slope is as low as 22.5 mV dec−1 for MoO x Rh-HNS revealing a hydrogen-spillover-involving HER mechanism proved by the electrochemical test as well as operando electrochemical impedance spectroscopy. Density functional theory calculation indicates the adsorbed hydrogen on MoO x Rh promotes the water dissociation and balances the hydrogen binding strength to a moderate level. Simultaneously, the hierarchical nanosheet structure contributes a robust HER stability at 500 mA cm−2. This work offers a new methodology to construct a high-performance alkaline HER electrocatalyst with industrial-level current density. [Display omitted] • MoO x has been incorporated into Rh hierarchical nanosheets at atomic level. • MoO x Rh-HNS exhibit a 14.9-fold higher mass activity than Pt/C at –0.2 V vs. RHE. • Hydrogen spillover is found to assist HER catalysis for MoO x Rh-HNS. [ABSTRACT FROM AUTHOR]

H 2 -selective catalytic reduction is a promising NO x control technology owing to its high intrinsic activity at low temperatures. We investigated catalysts composed of Pd NPs fixed in ZSM-5, which demonstrated enhanced activity for NO reduction by H 2 at T ≤ 150 ℃, achieving over 95 % NO x conversion and N 2 selectivity at 100 ℃. This system was particularly suited for studying the influence of hydrogen spillover on NO reduction activity because the fixed Pd NPs cannot interact with NO, while ZSM-5 can mediate hydrogen spillover and activate NO away from the Pd NPs on the Brønsted acid sites. Quantifying the kinetic isotope effect, and using catalytic measurements and in-situ infrared spectroscopy, we elucidate the reaction mechanism governing the catalytic activity. Under reaction conditions (NO + O 2 flow at 100 ℃), it was found that NO is activated as nitrosyl complexes on in-situ formed Pd cations as well as charge-compensating NO+ species at the cation exchange sites of ZSM-5, with the latter species serving as active intermediates. At this stage, the activated NO+ species on Brønsted acid sites undergo selective reduction to N 2 by reacting with spillover hydrogen from Pd NPs. Furthermore, the fixed Pd structure reduces the susceptibility to O 2 chemisorption, enabling the Pd NPs to preserve their metallic state against oxidative poisoning for efficient H 2 dissociation. Our study provides insights into the characterization of zeolite-fixed metal NPs, which is distinct from conventional analyses that focus on exposed metal sites. Moreover, this study highlights the fixation of metal NPs on zeolites as an effective strategy for NO reduction by H 2. [Display omitted] • Fixation of Pd nanoparticles in zeolites enhance the catalytic performance for NO reduction by H 2 at low temperatures. • Fixation of Pd nanoparticles influences the NO activation pathway under reaction conditions. • NO+ species activated at the Brønsted acid sites react with H 2 by a kinetically relevant hydrogen spillover step. • The fixed structure preserves the metallic state of Pd nanoparticles in the presence of excess O 2. [ABSTRACT FROM AUTHOR]

Single-atom alloys (SAA) in which active metal atoms are atomically dispersed in an inert host possess unique geometric and electronic structures, and generally own higher catalytic performance than their monometallic counterparts. Whereas it is still challenging to facilely synthesize well-defined single atoms embedded in single crystals dominated with a specific active plane. Herein, we synthesized Pd single atoms anchored in triangular Cu nanosheets (Pd 1 Cu SAA) with dominant active (111) plane via wet chemical synthesis and galvanic replacement as a high-performance catalyst for the electrocatalytic hydrodehalogenation (ECHD) of the refractory tribromophenol. Based on intensive theoretical calculations and experimental work, a hydrogen spillover mechanism was firstly proposed and verified for the highly efficient and selective ECHD. Hydrogen spillover occurs from the hydrogen-rich Pd to the hydrogen-deficient Cu host with a marginal kinetic energy barrier due to the short reaction distance and the negligible interfacial resistance. Meanwhile, the strong metal-support interaction between Pd and peripheral Cu optimizes the adsorption of hydrogenated products to allow for the further catalytic reaction. Consequently, by decoupling the ECHD process into hydrogen adsorption, hydrogen spillover and hydrodebromination, Pd 1 Cu SAA as a tandem catalyst completely reduced tribromophenol with high phenol selectivity. The intrinsic catalytic activity of Pd and Cu in Pd 1 Cu SAA substantially outperforms their monometallic counterparts by 14.4 and 3.2 times, respectively. This work showcases that the atomic dispersion of noble metals in SAA offers a promising catalyst design strategy to attain unprecedented catalytic properties via isolating activation and desorption steps. [Display omitted] • Single-atom alloys (Pd 1 Cu SAA) have been successfully synthesized. • Pd 1 Cu SAA dominated with the (111) active plane showed high catalytic performance. • Pd 1 Cu SAA exhibited higher intrinsic catalytic activity than their counterparts. • A hydrogen spillover mechanism was firstly proposed and verified. [ABSTRACT FROM AUTHOR]

The NiMgAl-layered double hydroxides, with the stoichiometric ratios of Mg/Ni and Mg/Al being 0–9 and 0–3, respectively, were synthesized and employed as the Ni catalyst precursors for NH 3 decomposition. The resulting catalyst of the certain Ni, Mg, and Al contents showed high catalytic efficiency and outstanding durability for the target reaction. The features of cost effective (with only Mg and Al elements besides Ni), easy fabrication, and thermally durable are attractive for large-scale operation. The characterizations revealed the related changes in structure and property, such as the Ni particle size and distribution, the reduction of Ni 2+ species, the Ni-oxide matrix interaction, the surface basicity as well as the adsorption/desorption behavior of hydrogen, in line with the stoichiometry of Ni, Mg, and Al in the samples. The superior catalytic activity and stability are thought to be associated with the structurally isolated active Ni species by the oxide matrix and the synergism between Ni-Mg sites. Particularly, the “spillover effect” of surface hydrogen accounts for a higher turnover frequency. [ABSTRACT FROM AUTHOR]

Polyethylene (PE) is one of the most environment-threatening plastic waste. Its Ru-catalyzed hydrogenolysis is rapid but produces too much methane. Here, low-density PE hydrogenolysis is performed at mild conditions and short times over Ru-doped zirconia catalysts (Ru-XZr, X = Ti, Nb, Ce, W, V, Mo, Fe) to determine low-methane catalysts. Methane is produced via direct terminal C-C scission and surface cascade of consecutive C-C scissions, with the latter sensitive to hydrogen availability and dominant in hydrogen-lean conditions. Reactivity studies, characterization and theory reveal that the most effective dopant oxides (W, V, and Mo) are intermediately reducible, as they store and supply extra hydrogen to Ru via reverse hydrogen spillover. This hydrogen readily hydrogenates and desorbs long alkyl surface intermediates that would otherwise produce cascade methane. Our proposed mechanism reconciles the low methane production achieved by increasing the hydrogen pressure or reducing the particle size and exposes the key selectivity descriptors. Ru-catalyzed LDPE hydrogenolysis is rapid but produces too much methane. Ru-doped zirconia catalysts with intermediately reducible dopant oxides suppress methane because they store and supply extra hydrogen to Ru via reverse hydrogen spillover. This hydrogen readily hydrogenates and desorbs long alkyl surface intermediates that would otherwise produce cascade methane. [Display omitted] • LDPE hydrogenolysis is performed over Ru-XZr to determine low-methane catalysts. • Two CH 4 -producing pathways are identified and investigated using surrogate reaction. • Intermediately reducible dopants suppress methane based on a volcano correlation. • A C-C scission cascade dominates CH 4 production, and is sensitive to H/Ru coverage. • Promotional dopants store and supply extra hydrogen to Ru via reverse spillover. [ABSTRACT FROM AUTHOR]

Co 2 Mo 10 /Co x /Al 2 O 3 catalysts were synthesized from the ammonium salt of [Co 2 Mo 10 O 38 H 4 ] 6− anion supported on alumina modified with various amount of cobalt sulphide. The catalysts were analyzed using X-ray powder diffraction, N 2 physisorption, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The catalysts were tested in the hydrodesulphurization (HDS) of dibenzothiophene and 4,6-dimethyldibenzothiophene and the hydrodenitrogenation (HDN) of quinoline. The presence of cobalt sulphide particles on the catalysts surface affects catalytic properties significantly, whereas the structure of the active phase remains constant. The catalytic activity, selectivity and turnover frequency during the HDS and HDN reactions depend on the amount of modifier (cobalt sulphide) in the Co x /Al 2 O 3 supports and can be explained by hydrogen spillover effect. The model of HDS reaction over Co 2 Mo 10 /Co x /Al 2 O 3 catalyst involving hydrogen spillover was established. The obtained results allow us to focus attention on the role of the cobalt sulphide particles on the surface of hydrotreating catalysts. [ABSTRACT FROM AUTHOR]

The mesocellular silica foams (MCF) supported rhodium catalysts, prepared by wetness impregnation method, were tested in CH 4 reforming with CO 2 . Hydrogen temperature-programmed desorption (H 2 -TPD) analysis showed that hydrogen spillover occurs on MCF loaded with highly dispersed rhodium. The turnover frequency of CH 4 (TOF CH4 (s −1 )) increased with the strength rise of spilt-over hydrogen. The promotion mechanism was investigated by controlled atmosphere 13 C and 1 H MAS NMR. The spilt-over hydrogen atoms were found to adsorb on the bridged oxygen sites (Si O Si) of MCF and to form surface terminal silanol groups. Meanwhile, in the reforming reaction steps, CH 4 dissociation into CH 3 * and CH 3 O* decomposition into CH 2 O* occurred. The results confirmed that hydrogen atoms can spill over from highly dispersed rhodium species to the neighboring bridged oxygen atoms of MCF, which promotes the reaction by facilitating rate determining steps of CH 4 dissociation and CH x O*( x = 2, 3) intermediates decomposition on metal surface. [ABSTRACT FROM AUTHOR]

Abstract: Pt supported on amorphous silico alumina (Pt/ASA) was studied as a catalyst for glycerol hydrogenolysis (dehydration+hydrogenation) to 1,2-propanediol under mild operation conditions (493K and 45bar H2 pressure). Glycerol hydrogenolysis also took place in experiments performed under N2 pressure due to hydrogen available from glycerol aqueous phase reforming. As both acid and metallic sites are involved in this process a study including activity tests and different characterization techniques (TPR and FTIR of adsorbed pyridine, NH3-TPD, XPS and TGA) were applied to this catalytic system (ASA support and Pt/ASA catalyst) in order to get a deeper understanding about their interactions. [Copyright &y& Elsevier]

Abstract: The effects of H2O on the performance of a model Pt/Ba/Al2O3 catalyst and regeneration of the catalyst surface were investigated, both in the absence and presence of CO2. In the absence of CO2, an unexpected promotional effect of H2O was observed at low temperature. For example, in the presence of H2O, 90% NO X conversion was obtained at 150°C, which is the same as that at 350°C under otherwise identical conditions. The results demonstrate that regeneration, the rate-limiting step at low temperature, occurs through hydrogen spillover to the nitrates, and not through reverse NO X species migration to the Pt sites, and the presence of H2O greatly promotes the hydrogen spillover rate by providing and stabilizing surface hydroxyl groups. The promotional effect of H2O gradually decreases with increasing temperature, and shows no positive effect above 350°C. In the presence of CO2, however, the presence of H2O always results in improved performance in the entire temperature range. Besides enhanced hydrogen spillover, another contribution of H2O when CO2 is present, is to weaken the detrimental effect of CO. CO is formed via the reverse water–gas shift reaction and poisons Pt sites as well as forms barium isocyanates. The H2O decreases the amount of CO formed as well as hydrolyzes the –NCO species. [Copyright &y& Elsevier]

The present work has provided new fundamental information on the effects of aging (mileage, km) of a commercial Pd-Rh (9:1, w/w) three-way catalyst (TWC) on (a) the H2 chemisorption, (b) the redox properties of washcoat material, and (c) the dynamic oxygen storage and release properties of TWC. Hydrogen chemisorption in the 25–400°C range was found to decrease with increasing aging of TWC. On the other hand, H2 chemisorption performed at 200 and 400°C resulted in a significantly larger amount of chemisorbed hydrogen (exceeding the monolayer value based on the noble metals) compared to that obtained after chemisorption at 25°C. This is due to the onset of a hydrogen spill over process in the 200–400°C range. The features of H2-TPD spectra were found to strongly depend on the aging of TWC. Hydrogen chemisorption at 25°C followed by TPD after a given pre-treatment of the catalyst surface might be considered as a procedure for a good estimate of the metal dispersion of a commercial Pd-Rh TWC. The redox properties of the oxygen storage components of the washcoat of a commercial Pd-Rh TWC were found to drastically change with increasing aging of TWC. It was found that the oxygen storage capacity (OSC) of the TWC investigated decreases significantly with catalyst aging in the 0–56,000km range and in the temperature range of 500–750°C. In the case of fresh TWC, the presence of 20ppm SO2 or 10% CO2 in a 1.5% O2/He gas mixture used for oxygen storage (oxidizing gas) was found to result in a large decrease in the amount of dynamic OSC measured by alternating switches between oxidizing and reducing feed gas compositions. The shift in time of the peak maximum of the transient response of CO2 obtained during the switch O2/He → He → CO/He (t) can be ascribed to the alteration of the kinetics of the oxygen back-spillover process and not to the kinetics of CO oxidation on the metal surface. [Copyright &y& Elsevier]

Hydrogen (H) spillover happened from Cu0 to SiO 2 , promoting RWGS reaction and thus CO formation. The contribution of H spillover to RWGS reaction can be controlled by the distance of Cu or coverage of surface hydroxyls on SiO 2 , which shifted the product selectivity from CO to CH 3 OH. [Display omitted] • A novel distance effect of Cu is discovered on Cu-based catalyst for CO 2 hydrogenation, boosting CH 3 OH and CH 3 OCH 3 selectivity from 36 to 89 mol%. • H spillover from Cu to SiO 2 is identified, which can be regulated by the distance of Cu. • The regulation of H spillover restrains reverse water gas shift reaction and CO formation, which highlights CH 3 OH and CH 3 OCH 3 selectivity. It is desirable but challenging to obtain high methanol selectivity in CO 2 hydrogenation on Cu/ZnO catalysts. Herein, we dispersed a commercial Cu/ZnO/Al 2 O 3 on a silica support for CO 2 hydrogenation to methanol, and discovered by high-angle annular dark-field scanning transmission electron microscopy (HADDF-STEM) that the distance between Cu nanoparticles on silica tuned the total methanol selectivity from 35.5 mol% to 88.9 mol%. This distance effect of Cu was elucidated by H 2 -TPR, FT-IR, in situ DRIFT, and catalyst silylation modification. It was identified that the active hydrogen species produced on Cu diffuse onto silica via the surface silanols, promoting reverse water gas shift (RWGS) reaction to produce CO. The average concentration of spilled hydrogen species was decreased along with the distance of Cu on silica, suppressing RWGS reaction and thus highlighting methanol selectivity. We anticipate that the distance effect observed here is prevalent on metal supported catalysts in other (de)hydrogenation reactions. [ABSTRACT FROM AUTHOR]

• TOF MeOH increases with an increase in CO 2 content of the CO 2 /CO feed. • TOF MeOH ratio of (TOF) 5%CO2 /(TOF) 100%CO2 were 1.8 for Cu 6 Zn 3.0 Zr 0.0 Al 1. • TOF MeOH ratio of (TOF) 5%CO2 /(TOF) 100%CO2 were 10.4 for Cu 6 Zn 0.0 Zr 3.0 Al 1. • The role of ZrO 2 is enhanced by the reverse hydrogen spillover of Cu/ZnO. • The role of ZrO 2 is important only for high CO2 feed more than 50%. This work investigates the promotional roles of ZrO 2 and ZnO for methanol synthesis on five Cu 6 Zn 3.0-x Zr x Al 1 (x = 0.0, 0.5, 1.5, 2.5, 3.0) catalysts in the various CO 2 feed composition. TOF decreased with an increase in x of Cu 6 Zn 3.0-x Zr x Al 1 catalysts in the 5% CO 2 feed, while TOF is maximized over Cu 6 Zn 1.5 Zr 1.5 Al 1 in the 100% CO 2 feed. Both the effects of Zn (reverse spillover) and Zr (additional reaction sites) in the vicinity of Cu promote the CO 2 hydrogenation, maximizing the catalytic activity of Cu 6 Zn 1.5 Zr 1.5 Al 1 in the 100% CO 2 feed. The migration of hydrogen on ZrO 2 can be limited in little surface hydroxyls in 5% CO 2 feed, which can be a reason for the negative role of ZrO 2 in the 5% CO feed. The promotional effect of ZrO 2 on Cu/ZnO is important only for high CO 2 feed more than 50% CO 2. [ABSTRACT FROM AUTHOR]